1. Field of the Invention
The present invention relates to a liquid crystal panel, and particularly, to a liquid crystal panel device that prevents over-filling of liquid crystal material.
2. Description of the Background Art
Currently, development of various portable electric devices, such as mobile phones, personal digital assistants (PDA), and notebook computers, has increased. Accordingly, different flat panel display devices such as liquid crystal display (LCD), plasma display panel (PDP), field emission display (FED), and vacuum fluorescent display (VFD) devices are being developed. The LCD devices display information on a screen using refractive anisotropy of liquid crystal material.
FIG. 1 is a cross sectional view of a liquid crystal display device according to the related art. In FIG. 1, a liquid crystal panel 1 comprises a lower substrate 5, an upper substrate 3, and a liquid crystal material layer 7 formed between the lower substrate 5 and the upper substrate 3. The lower substrate 5 is a driving device array substrate, and includes a plurality of pixels (not shown), wherein a driving device, such as a thin film transistor (TFT), is formed on each pixel. The upper substrate 3 is a color filter substrate, and includes a color filter layer (not shown) for reproducing real color. In addition, a pixel electrode (not shown) and a common electrode (not shown) are formed on the lower substrate 5 and the upper substrate 3, respectively. An alignment layer (not shown) is formed on the lower substrate 5 and the upper substrate 3 to uniformly align liquid crystal molecules of the liquid crystal material layer 7.
The lower substrate 5 and the upper substrate 3 are attached by a sealing material 9, and the liquid crystal material layer 7 is formed therebetween. In addition, the liquid crystal molecules are reoriented by the driving device formed on the lower substrate 5 to control the amount of light transmitting through the liquid crystal material layer 7, thereby displaying an image.
Fabrication processes for an LCD device may be divided into a TFT array substrate process for forming the driving device (TFT) on the lower substrate 5, a color filter substrate process for forming the color filter on the upper substrate 3, and a cell formation process. The cell formation process includes attaching the TFT substrate 5 and the color filter substrate 3, forming the liquid crystal material layer 7 therebetween, and treating to this form the liquid crystal display panel 1. Generally, the liquid crystal material layer 7 is formed by a liquid crystal dipping method or by a liquid crystal vacuum injection method. Either one of the liquid crystal dipping method or the liquid crystal vacuum injecting method is performed after the TFT substrate 5 and the color filter substrate 3 are attached and treated.
FIG. 2 is a cross sectional view of a liquid crystal injection process according to the related art. In FIG. 2, a container 12 is filled with the liquid crystal material 14 and is disposed in a vacuum chamber 10, and a portion of a liquid crystal display panel 1 is positioned within the container 12. The vacuum chamber 10 maintains a vacuum pressure by connection to a vacuum pump (not shown). Although it is not shown, a device for moving the liquid crystal display panel 1 is installed within the vacuum chamber 10 to move the liquid crystal display panel 1 from an upper part of the vacuum chamber 10 to the container 12. In addition, an injection hole 16 is formed on the liquid crystal display panel 1 to contact the liquid crystal material 14.
When the vacuum pressure within the chamber 10 is reduced, the injection hole 16 of the liquid crystal display panel 1 is placed into the container 12. Accordingly, the liquid crystal material 14 is injected into the liquid crystal display panel 1 through the injection hole 16 due to a difference between pressure within the liquid crystal display panel 1 and the vacuum pressure of the vacuum chamber 10. The injection hole 16 is sealed using a sealing material after the liquid crystal material 14 is completely filled into the liquid crystal display panel 1, thereby forming the liquid crystal material layer 7 (in FIG. 1).
However, the method of forming a liquid crystal material layer by injecting the liquid crystal material 14 through the injection hole 16 of the liquid crystal display panel 1 in the vacuum chamber 10 may be problematic. First, injection of the liquid crystal material 14 into the liquid crystal display panel 1 may be time consuming. In general, a narrow gap of a few μm is commonly provided between the driving device array substrate and the color filter substrate of the liquid crystal display panel 1 such that a very small amount of liquid crystal material 14 may be injected into the liquid crystal display panel 1 per unit of time. For example, in order to fabricate a 15 inch liquid crystal display panel 1, it takes about 8 hours to completely inject the liquid crystal material 14. Accordingly, the overall fabrication process for making the liquid crystal display panel 1 is increased due to the time for completing the liquid crystal injection process, thereby lowering fabrication efficiency.
Second, consumption of the liquid crystal material is increased as a result of the liquid crystal injection method. For example, a very small amount of the liquid crystal material 14 in the container 12 is actually injected into the liquid crystal display panel 1. In addition, when the liquid crystal material 14 is exposed to an ambient atmosphere or to certain gases, the liquid crystal material 14 deteriorates due to the reaction with the gases. Accordingly, the liquid crystal display panel 1 deteriorates by exposure to impurities within the liquid crystal material 14. Thus, any liquid crystal material 14 remaining in the chamber 12 after the injection process is completed must be discarded, thereby increasing fabrication costs.
One proposed solution to the above problems includes a liquid crystal dropping method for forming the liquid crystal material layer. The liquid crystal dropping method includes procedures for dropping and dispensing the liquid crystal material directly onto a display panel area of a first substrate, thereby uniformly distributing the dropped liquid crystal material across an entire panel area during attachment of a second substrate to the first substrate. Accordingly, the liquid crystal material is directly dropped onto the first substrate during a relatively short amount of time, and thus, the liquid crystal material layer in a large-sized LCD may be rapidly formed.
FIG. 3 is a cross sectional view of a liquid crystal dropping method according to the related art, and FIG. 4 is a plan view of a method for fabricating a liquid crystal material layer using a liquid crystal dropping method according to the related art. In FIG. 3, a drop shaped liquid crystal material 14 is dropped onto a surface of a TFT substrate 5 prior to a bonding process with a color filter substrate 3. The liquid crystal material 14 is dropped by a liquid crystal dispensing apparatus 20, as shown in FIG. 4. Although it is not shown in the figures, a system for controlling a dropping amount of the liquid crystal material 14 is disposed in the liquid crystal dispensing apparatus 20. Accordingly, since the TFT substrate 5 is able to move along x- and y-directions, the liquid crystal material 14 is dispensed at uniform intervals across the surface of the TFT substrate 5.
In FIG. 3, a sealing material 9 is applied along an outer perimeter portion of the color filter substrate 3. Then, the color filter substrate 3 and the TFT substrate 5 are bonded together by pressing the color filter substrate 3 and the TFT substrate 5 together, thereby uniformly distributing the liquid crystal material 14 between the color filter substrate 3 and the TFT substrate 5. Accordingly, one distinguishing characteristic of the liquid crystal dropping method is that the liquid crystal material 14 is dropped onto the surface of the TFT substrate 5 before the liquid crystal display panel 1 is fabricated.
However, the liquid crystal dropping method may be problematic. For example, although a set amount of the liquid crystal material 14 is determined by the liquid crystal dispensing apparatus 20, deviations between the set amount and the amount actually dropped onto the surface of the TFT substrate 5 may occur, thereby causing significant problems. For example, when the actual amount of liquid crystal material 14 is less than the set amount, black brightness during a normally black mode and white brightness during a normally white mode are compromised. Conversely, when the actual amount of the liquid crystal material 14 is greater than the set amount, a gravity failure is generated within the liquid crystal display panel 1. The gravity failure is generated when a volume of the liquid crystal material 14 formed within the liquid crystal display panel 1 increases due to an increase in temperature. Accordingly, a cell gap of the liquid crystal display panel 1 increases by an amount greater than a spacer formed between the color filter substrate 3 and the TFT substrate 5.